What is the therapeutic index?

The therapeutic index is a critical measure used to evaluate the safety and efficacy of a drug. It is specifically defined as the ratio of the lethal dose for 50% of a population (LD50) to the effective dose for 50% of a population (ED50). This ratio provides insight into the margin of safety of a drug; a higher therapeutic index indicates a wider margin between effective and lethal doses, suggesting that the drug can be used safely at dose levels that are effective without reaching toxicity.

In this context, the choice that states LD50/ED50 appropriately captures this relationship, showing the balance between the doses that lead to therapeutic effects versus those that cause toxicity. Understanding the therapeutic index is essential in pharmacology because it helps in determining appropriate dosing regimens and ensuring patient safety while achieving therapeutic goals.